Create a standalone legend for edge glyphs

Builds a standalone legend explaining the glyphs drawn at edge ends. Glyphs are not mapped to 'ggplot2' aesthetics, so they never appear in a 'ggplot2' legend; this function draws each key with the same renderer used for edges and returns it as a 'grob' object that can be added to a plot.

Usage

glyph_legend(
  arrowType,
  legend_title = NULL,
  glyph_size = 3,
  key_width = 12,
  text_size = 10,
  colour = "grey20",
  linewidth = 0.5,
  orientation = c("vertical", "horizontal"),
  ncol = NULL
)

Arguments

arrowType

A named vector of arrowType codes, written as for edges; names become legend labels. Codes may be integer codes (e.g. 1, -1), basic token codes (e.g. "-->", "<->"), or extended token codes (e.g. "01<->01"); a bare token is read as the end glyph (e.g. ">01"). See glyph_list for the available tokens.

legend_title

The legend title, or NULL for no title.

glyph_size

Glyph size, in mm.

key_width

Width of each key (the edge sample), in mm. It should be large enough to hold the glyphs at both ends, e.g. at least 4 * glyph_size.

text_size

Text size, in points.

colour

Edge and glyph colour: one value, or one per key.

linewidth

Edge and glyph line width, in mm: one value, or one per key.

orientation

Legend arrangement ("vertical" or "horizontal"): the order in which keys fill the columns. Vertical fills each column top to bottom; horizontal fills each row left to right.

ncol

Number of columns of keys. Defaults to 1 for a vertical legend and to one column per key (a single row) for a horizontal one.

Value

A 'gtable' object of class 'gspace_legend', which can be drawn with plot() or grid::grid.draw(), or added to a ggplot with 'patchwork'.

Examples

library(ggplot2)

# Show the whole glyph collection, arranged in three columns
glyphs <- glyph_list()
leg1 <- glyph_legend(glyphs$token, ncol = 3, 
        legend_title = "Edge glyph collection")
plot(leg1)


# Build a legend from named arrowType codes; names become labels
tokens <- c(Activation = "-->", Inhibition = "--|", Complex = "03|-|05")
leg2 <- glyph_legend(tokens, legend_title = "Interaction")
plot(leg2)


# Add a glyph legend to a plot (requires patchwork)
if (requireNamespace("patchwork", quietly = TRUE)) {
  p <- ggplot(mtcars, aes(wt, mpg)) + geom_point()
  p + leg2 + patchwork::plot_layout(widths = c(1, 0.5))
}